Ataxia-ocular apraxia 2 (AOA2), or ataxia with oculomotor apraxia type 2, is a recently identified autosomal recessive cerebellar ataxia (Le Ber, I. et al., Curr. Neurol. Neurosci. Rep. 2005, 5(5):411-7). Initially associated with a locus at 9q34 (Bomont, P. et al., Eur. J. Hum. Genet. 2000, 8:986-990; Nemeth, A. H. et al., Am. J. Hum. Genet. 2000, 67:1320-1326; Le Ber, I. et al., Brain 2004, 127: 759-767; Izatt, L. et al., J. Neurol. 2004, 251:805-812; Mahajnah, M. et al., J. Child Neural. 2005, 20(5):523-525), AOA2 has now been linked to mutations in the senataxin (SETX) gene at that locus (Moreira, M-C. et al., Nat. Genet. 2004, 36(3):225-227; Duquette, A. et al., Ann. Neurol. 2005, 57:408-414). Certain mutations in the 9q34 locus, including mutations in the SETX gene, have also been associated with an autosomal dominant juvenile amyotrophic lateral sclerosis (ALS4) (Chance, P. F. et al., Am. J. Hum. Genet. 1998, 62:633-640; Rabin, B. A. et al., Brain 1999, 122:1539-1550; Blair, I. P. et al., Neurogenetics 2000, 3:1-6; Chen, Y.-Z. et al., Am. J. Hum. Genet. 2004, 74:1128-1135). In addition, AOA2 shares some similarities with other autosomal recessive cerebellar ataxias (ARCAs), including ataxia-telangiectasia (A-T) (Chun, H. H. And R. A. Gatti, DNA Repair, 2004, 3:1187-1196) and ataxia with oculomotor apraxia type I (AOA1) (Le Ber, I. et al., Brain 2003, 126:2761-2772). A need remains for means to distinguish AOA2 from other diseases, and particularly from ALS4 and AOA1.